Conceptually I understand that mass is a measure of the amount of stuff present in an object, while weight is a measure of the force of gravity applied to that object. An object of a given mass will have a bigger weight on Earth than on the moon because Earth’s gravity is stronger. But… mass is determined by weighing an object on a scale. And there is a simple mathematical conversion between grams (mass) and pounds (weight), implying that they’re just different units for the same concept. So what gives? (Also this is a question that applies to so many fields, I had no idea which flair to apply.)
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Grams and pounds are just the metric and imperial units of mass. They measure the same thing.
Bathroom scales don’t actually measure mass, they measure pressure. They’re marked in kg or lb because they’re calibrated for Earth’s gravity and the conversion is simple between kg (mass) and N/m2 (pressure). They could be marked in N/m2 (but then you’d need to account for the area of the person’s footprint), or just Newtons. We’re used to using units of mass, so they’re marked in those.
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